fix: cpp rules now properly respect the language attribute

[avrabe]

Fixes #211

Summary

This PR resolves the issue where C/C++ component rules were ignoring the language attribute and always generating C bindings regardless of user configuration.

Root Cause

The cpp_component and cpp_wit_bindgen rules had hardcoded "c" values in their binding generation code, completely ignoring the ctx.attr.language attribute.

Changes

Core Fixes

1. cpp/defs.bzl:157 - Fixed cpp_component to use ctx.attr.language instead of hardcoded "c"
2. cpp/defs.bzl:628 - Fixed cpp_wit_bindgen to use ctx.attr.language instead of hardcoded "c"
3. cpp/defs.bzl:305-306 - Fixed binding file extensions to match language (.c vs .cpp)
4. cpp/defs.bzl:116-119 - Added C++ source auto-detection for compilation support
5. cpp/defs.bzl:340-359 - Added C++ include paths and compilation flags for C++ bindings
6. cpp/defs.bzl:664-666 - Fixed --string-encoding to only apply to C bindings
7. cpp/defs.bzl:497-505 - Added cxx_std and optimization to WasmComponentInfo metadata
8. cpp/defs.bzl - Updated all action mnemonics to be language-specific

Test Framework Improvements

1. test/cpp/cpp_component_tests.bzl:135-149 - Fixed bindings test to check for directory
2. test/cpp/cpp_component_tests.bzl:338-347, 404-407 - Fixed optional optimization attribute handling
3. test/cpp/BUILD.bazel:117-125 - Updated test expectations to use integer values

Example Updates

1. examples/cpp_component/multi_component_system/BUILD.bazel - Fixed auth_service_cpp to use language="c"
2. examples/cpp_component/data_structures/BUILD.bazel - Fixed data_structures_component to use language="c"
3. examples/cpp_component/http_service/BUILD.bazel - Added explicit language="c" and optimize=True
4. examples/cpp_component/simple_calculator/simple_calculator.cpp - Demonstrates true C++ bindings

Architecture Patterns

This PR establishes three clear patterns:

1. C++ source with C bindings: Set language="c" - auto-detection enables C++ compilation, generates C-style API
2. C++ source with C++ bindings: Set language="cpp" - generates namespace-based C++ API
3. C source with C bindings: Set language="c" - standard C compilation and bindings

Test Results

✅ All 19 C/C++ tests passing
✅ All C/C++ examples building successfully

Verification

# Run all C/C++ tests
bazel test //test/cpp:all_cpp_tests

# Build all examples
bazel build //examples/cpp_component/...

Breaking Changes

None - this fix makes the rules work as originally intended. Users who were relying on the buggy behavior (hardcoded C bindings) may need to add explicit language="c" to their targets if not already specified.